This advisory expires tonight at 12:00 midnight.
Tuckerman and Huntington Ravines will have Considerable avalanche danger. Natural avalanches are possible and human triggered avalanches are likely. Dangerous avalanche conditions will exist.
AVALANCHE PROBLEM: The Wind Slab avalanche problem discussed yesterday will begin as the first issue today. A rising temperature and rain showers will increase the potential for Wet Slab problems later this afternoon acting as the secondary problem. Although coming second in timing it will be the first problem regarding hazard and is the main factor for the Considerable rating today. Based on the current expectations of weather, the greatest potential for natural wet slab avalanches will be as we move through the late afternoon and into darkness when rainfall is expected to increase. However, pay attention to warming and rain earlier in the day. Warm air temperatures and rain on cold wind slab is a definite red flag requiring very careful terrain management to negotiate natural wet slab issues.
WEATHER: Temperatures are climbing quickly and the mid elevations are already deep into the 40’sF! The 4000 foot level is already at almost 46F, with typical avalanche start zones hovering between 40-42F. Rain is forecasted to work into our terrain in the afternoon and then pick up in potential around dinner time. Periods of heavy rain are anticipated overnight with some thundershowers. Very high winds are associated with this precipitation event, gusting over 100mph very late today. Rain and high winds will continue tomorrow on the summits making for a very unpleasant day for alpine travel.
SNOWPACK: The danger ratings for today are related to the near surface cold hard slabs that developed early Tuesday becoming warm and wet. The rapid temperature increase and eventual rain will effect these areas of wind slab, causing the potential for natural avalanches to rise. We have very little concern for the hard frozen snowpack that is below these recent wind slabs from 48 hours ago as they stabilized through earlier rain and several melt freeze cycles. The new slabs we are concerned about today are not spatially widespread and several forecast area ratings are a bit conservative based on limited knowledge of new slab coverage. We will be going through another “reset button” hit over the next 24 hours with about 0.5-.75″ of rain on our snowpack. When we say “reset” it refers to an event that dramatically reduces or eliminates instability concerns in the current snowpack. However, until we make it through this rain event we must endure a spike in snow instability which we will see over the next 24 hours. Having a conservative approach in these kind of weather conditions is important when considering to travel in avalanche terrain. I would avoid the runouts under areas of recent slabs, likely being a brighter white than the older grey surface.
Other spring hazards that are significant threats today:
- Crevasses, moats and waterfall holes – Water flowing under the snow pack creates holes and thin spots in surface snow that are deep enough to injure or ….worse.
- Falling Ice. Lunch Rocks and the floor are in the bullseye. Lunch Rocks, or “ICEFALL ROCKS”, gets hammered by ice every season it is not a good place to hang out. This location for many serious injuries over the years.
- Safe travel in avalanche terrain requires training and experience. This advisory is just one tool to help you make your own decisions in avalanche terrain. You control your own risk by choosing where, when, and how you travel.
- Anticipate a changing avalanche danger when actual weather differs from the higher summits forecast.
- For more information contact the Forest Service Snow Rangers, the AMC at the Pinkham Notch Visitor Center, or the caretakers at Hermit Lake Shelters or the Harvard Cabin.
- Posted 7:35 a.m., Thursday, March 31, 2016. A new advisory will be issued tomorrow.
Christopher Joosen, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2716